Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Life habit: non-lichenized Thallus: inconspicuous, mycelial, with hyphae disrupting bark surface photobiont: not present Ascomata: circular to unbranched lirellate, immersed to semi-sessile, 0.1-0.5 mm wide, 70-100 µm tall disc: black, becoming convex, pruinose epihymenium: olivaceous brown, 15-20 µm thick hymenium: hyaline, 30-40 µm tall; paraphysoids: hyaline, smooth, with hyphae c. 1 µm wide, in a gel; subhymenium: hyaline, 15-25 µm thick; end cells of paraphysoids up to 3 µm thick asci: broadly clavate, without distinct stipe, 25-35 x 13-16 µm ascospores: persistently hyaline, 3-septate (not incised), narrowly ovoid, 12-15 x 4-5 µm, septal ontogeny unidirectional, without an epispore Pycnidia: c. 0.1 µm wide, upper part olivacous brown conidia: filiform, curved, 9-11(-13) x 1 µm Chemical reactions: ascomatal gels I+ blue-red or persistently blue, KI+ blue; ascus tholus with KI+ ring-structure; epispore I-, KI- Secondary metabolite: calcium oxalate abundant in the epihymenium. Substrate and ecology: on smooth bark of young branches of deciduous trees near the coast World distribution: North America and Europe Sonoran distribution: southern California (Los Angeles Co.), Baja California Sur, and Sonora.. Notes: Arthonia pruinosella is similar to A. stictoides, known from Europe, which differs mainly by having smaller ascomata, asci and spores. Arthonia tetramera lacks calcium oxalate in the epihymenium and differs by having narrowly lirellate ascomata and smaller microconidia.